The present invention relates to a pneumatic radial tire and, more specifically, to a pneumatic radial tire having runflat capability by providing, at the sidewall of the tire, a metal-reinforced ply and a circumferentially deployed insert, such that the tire is capable of being used in the uninflated condition.
Various methods have been devised for enabling the safe continued operation of unpressurized or underpressurized passenger-car tires without damaging the tire further and without causing poor steering, over a distance from the place where the tire lost its pressure to a place desired by the driver, such as a service station where the tire can be changed. Loss of tire pressure can result from a variety of causes, including puncture by a foreign object such as a nail or other sharp object piercing the pneumatic tire installed on a vehicle.
Pneumatic tires designed for continued operation under conditions of unpressurization or underpressuration are also called runflat tires, as they are capable of being driven in the uninflated condition. The conventional pneumatic tire when operated without inflation collapses upon itself when supporting a vehicle load. In general, the term xe2x80x9crunflatxe2x80x9d means that the tire structure alone has sufficient strength to support the vehicle load when the tire is operated in the uninflated condition such that the sidewall and internal surfaces of the tire do not collapse or buckle onto themselves, without recourse to incorporation of any internal support devices to prevent the tire from collapsing.
One approach to runflat tire design is described in U.S. Pat. No. 4,111,249, entitled the xe2x80x9cBanded Tire,xe2x80x9d in which a hoop or annular band approximately as wide as the tread was placed under the tread. The hoop in combination with the rest of the tire structure could support the vehicle weight in the uninflated condition. This banded tire actually tensioned the ply cords even in the uninflated condition.
Numerous other methods have been used to achieve workable runflat tire design. Generally, such tires incorporate sidewall designs that are thicker and/or stiffer, so that the tire""s load can be carried by an uninflated tire without otherwise compromising vehicle handling until such reasonable time as the tire can be repaired or replaced. The methods used in sidewall stiffening include the incorporation of inserts or fillers generally having, in cross-sectional view, a crescent shape. Such inserts or fillers are located in the inner peripheral surface of the sidewall portion of the carcass, which is the region in the tire usually having the lowest rigidity. In such runflat tire designs, the entire sidewall has a crescent shaped cross-section so as to provide rigidity. The sidewalls of such tires, when operated in the uninflated condition, experience a net compressive load, though with outer portions of the sidewalls necessarily being in tension due to the bending deformation, especially in the regions of the sidewall adjacent to the ground-contacting portion of the tread. Due to the large amounts of rubber required to stiffen the sidewall members, heat buildup is a major factor in tire failure especially when the uninflated tire is operated for prolonged periods at high speeds.
A Goodyear patent (U.S. Pat. No. 5,368,082) disclosed the first commercially accepted runflat pneumatic radial ply tire, the relatively low-aspect-ratio, Eagle GSC-EMT tire. The U.S Pat. No. 5,368,082 teaches the employment of special sidewall inserts to improve stiffness. Approximately six additional pounds of weight per tire was required to support an 800 pound (lb) load in this uninflated tire. This earlier invention, although superior to prior attempts at runflat tire design, still imposed a weight penalty that could be offset by the elimination of a spare tire and the tire jack. However, this weight penalty was more problematic when the engineers attempted to build high-aspect-ratio, runflat tires for larger luxury sedans. The required supported weight for an uninflated luxury car tire approximates 1400 lbs. These taller sidewalled tires, having aspect ratios in the 55% to 65% range or greater, means that the sidewall bending stresses are several times that of the earlier low-aspect-ratio runflat Corvette type tires. Such loads meant that the sidewalls and overall tire had to be stiffened to the point of compromising ride. Being that luxury vehicle owners do not expect to sacrifice ride quality for runflat capability, the engineering requirements for runflat tire design require that there be no loss in ride or performance. In the very stiff suspension performance type vehicle, such as the Corvette and various sport/utility vehicles, the ability to provide such runflat tires was relatively straightforward compared to providing similar runflat tires for luxury sedans which require softer ride characteristics. Light truck and sport utility vehicles, although not as sensitive to ride performance, provide a runflat tire market that ranges from accepting a stiffer ride to demanding the softer luxury type ride.
Runflat tire design, as disclosed for example in U.S. patent application Ser. No. 08/865,489, entitled RUNFLAT TIRE WITH IMPROVED CARCASS, having a common assignee with the present invention and incorporated in its entirety by reference herein, is based on the installation of a plurality of heavy-ply wedge fillers or inserts inside each sidewall flex area. The inserts add rigidity to the sidewalls in the absence of air pressure during runflat operation. But while the high resistance to compression of the compound of the insert wedges provides the necessary resistance to the collapse of the loaded tire without air pressure, this method has several drawbacks. The two most important ones are heavy tire weight and heat buildup in the wedge inserts.
It is an object of the present invention to provide a pneumatic radial ply runflat tire, the tire as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
An object of the present invention is to provide a pneumatic radial runflat tire having good tire life and vehicle handling characteristics and a satisfactory ride, by incorporating a wire-reinforced innermost radial ply whose compression-load-bearing capabilities reduce the amount of insert material typically used in runflat tire designs.
Another object of the present invention is to provide a pneumatic radial runflat tire which can be constructed of two carcass plies, the innermost of which is reinforced by metal wire and the outermost being fabric reinforced, the two plies being separated in each sidewall by an insert disposed in the sidewall flex area.
Another object of the present invention is to provide a pneumatic radial runflat tire in which, when operating in a runflat condition, the outermost fabric ply supports tensile stresses while the wire-reinforced inner ply and a part of the insert, support compression stresses.
Still another object of the present invention is to provide a radial runflat tire which uses the high thermal conductivity of a wire-reinforced inner ply to redistribute the heat buildup in the insert during normal tire operation and, in particular, during runflat operation.
Yet another object of the present invention is to minimize heat buildup in the insert by using an inner wire-reinforced ply to carry a significant share of the compressive portion of the runflat load.
The present invention relates to a pneumatic radial ply runflat passenger tire having a tread, a casing with two sidewalls, two radial plies extending from two annular beads and a belt reinforcement structure located radially between the tread and the plies. The runflat sidewall design is characterized by an inner radial ply having metal reinforcement cords and an outer radial ply having organic fiber reinforcement cords. An insert is circumferentially disposed between the inner and outer plies in the region of each sidewall adjacent to the tread shoulder. The insert in each sidewall has properties characterized by high tensile strength, low hysteresis and light weight. The strength and rigidity of the insert can be adjusted by the incorporation of organic fibers aligned more or less in the radial direction within the insert. Metal reinforcing cords in the inner radial ply have properties characterized by a high modulus of elasticity, rigidity with respect to carrying the compressive load on the inserts during runflat operation, and good thermal conductivity which distributes heat generated within the inserts during runflat operation. During runflat operation, the high modulus of the reinforcing metal cords of the inner ply carry a substantial compressive load, thereby reducing the compression load carried by the single insert in each sidewall. Also during runflat operation, the outer organic-fiber reinforced ply has good flexibility accompanied by high tensile-stress-bearing capacity.
In one embodiment of the invention, the pneumatic radial runflat passenger tire has a low-profile design geometry suitable, aesthetically and/or pragmatically, for use on sports-type vehicles.
In another embodiment, the pneumatic radial ply runflat passenger tire has a high-profile design geometry suitable, aesthetically and/or pragmatically, for use on luxury vehicles and high-standing sport-utility vehicles.
Tire structure according to this invention incorporates adjustments to the composition of the insert in each sidewall as well as to the overall cross-sectional area of the metal reinforcements in the innermost ply in accordance with the intended usage in high-low- or intermediate-profile tire designs.